Environmental control system utilizing multiple mix points for recirculation air in accordance with pressure mode

ABSTRACT

A system is provided. The system includes an air conditioning pack; a first medium; a second medium; a first mixing point located outside the air conditioning pack and configured to mix the first medium with the second medium; and a second mixing point located inside the air conditioning pack and configured to mix the first medium with the second medium.

BACKGROUND

In general, with respect to present air conditioning systems ofaircraft, cabin pressurization and cooling is powered by engine bleedpressures at cruise. For example, pressurized air from an engine of theaircraft is provided to a cabin through a series of systems that alterthe temperatures and pressures of the pressurized air. To power thispreparation of the pressurized air, the only source of energy is thepressure of the air itself. As a result, the present air conditioningsystems have always required relatively high pressures at cruise.Unfortunately, in view of an overarching trend in the aerospace industrytowards more efficient aircraft, the relatively high pressures providelimited efficiency with respect to engine fuel burn.

SUMMARY

According to one embodiment, a system is provided. The system includesan air conditioning pack; a first medium; a second medium; a firstmixing point located outside the air conditioning pack and configured tomix the first medium with the second medium; and a second mixing pointlocated inside the air conditioning pack and configured to mix the firstmedium with the second medium.

Additional features and advantages are realized through the techniquesof the embodiments herein. Other embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed invention. For a better understanding of the invention withthe advantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A is a diagram of an schematic of an environmental control systemaccording to an embodiment;

FIG. 1B is a diagram of an schematic of a conventional bleed air drivenenvironmental control system of an airplane utilizing a contemporarycabin three-wheel air conditioning system;

FIG. 2 is operation example of an environmental control system accordingto an embodiment;

FIG. 3 is operation example of an environmental control system accordingto another embodiment;

FIG. 4 is operation example of an environmental control system accordingto another embodiment; and

FIG. 5 is operation example of an environmental control system accordingto another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the FIGS.

Embodiments herein provide an environmental control system that utilizesbleed pressures near a cabin pressure to power the environmental controlsystem, along with mixing recirculation air mixed at different locationswithin the environmental control system in accordance with a pressuremode, to provide cabin pressurization and cooling at a high engine fuelburn efficiency.

In general, embodiments of the environmental control system may includeone or more heat exchangers and a compressing device. A medium, bledfrom a low-pressure location of an engine, flows through the one or moreheat exchangers into a chamber. Turning now to FIG. 1A, a system 100that receives a medium from an inlet 101 and provides a conditioned formof the medium to a chamber 102 is illustrated. The system 100 comprisesa compressing device 120 and a heat exchanger 130. The elements of thesystem are connected via valves, tubes, pipes, and the like. Valves(e.g., flow regulation device or mass flow valve) are devices thatregulate, direct, and/or control a flow of a medium by opening, closing,or partially obstructing various passageways within the tubes, pipes,etc. of the system 100. Valves can be operated by actuators, such thatflow rates of the medium in any portion of the system 100 can beregulated to a desired value.

As shown in FIG. 1A, a medium can flow from an inlet 101 through thesystem 100 to a chamber 102, as indicated by solid-lined arrows A, B. Inthe system 100, the medium can flow through the compressing device 120,through the heat exchanger 130, from the compressing device 120 to theheat exchanger 130, from the heat exchanger 130 to the compressingdevice 120, etc. Further, the medium can recirculate from the chamber102 to the system 100, as indicated by the dot-dashed lined arrow D (andcan then flow back to the chamber 102 and/or external to the system100).

The medium, in general, can be air, while other examples include gases,liquids, fluidized solids, or slurries. When the medium is beingprovided from the chamber 102 of the system 100, the medium is referredto herein as recirculated air. When the medium is being provided by anengine connected to the system 100, such as from the inlet 101, themedium can be referred to herein as bleed air (also known as fresh airor outside air). With respect to bleed air, a low-pressure location ofthe engine (or an auxiliary power unit) can be utilized to provide themedium at an initial pressure level near a pressure of the medium onceit is in the chamber 102 (e.g., chamber pressure, also referred to ascabin pressure in the aircraft example).

For instance, continuing with the aircraft example above, air can besupplied to the environmental control system by being “bled” from acompressor stage of a turbine engine. The temperature, humidity, andpressure of this bleed air varies widely depending upon a compressorstage and a revolutions per minute of the turbine engine. Since alow-pressure location of the engine is utilized, the air may be slightlyabove or slightly below cabin pressure (e.g., the pressure in thechamber 102). Bleeding the air at such a low pressure from thelow-pressure location causes less of a fuel burn than bleeding air froma higher pressure location. Yet, because the air is starting at thisrelatively low initial pressure level and because a drop in pressureoccurs over the one or more heat exchangers, a pressure of the air maydrop below the cabin pressure while the air is flowing through the heatexchanger 130. When the pressure of the air is below the cabin pressure,the air will not flow into the chamber to provide pressurization andtemperature conditioning. To achieve the desired pressure, the bleed-aircan be compressed as it is passed through the compressing device 120.

The compressing device 120 is a mechanical device that controls andmanipulates the medium (e.g., increasing the pressure of bleed air).Examples of a compressing device 120 include an air cycle machine, athree-wheel machine, a four wheel-machine, etc. The compressing caninclude a compressor, such as a centrifugal, a diagonal or mixed-flow,axial-flow, reciprocating, ionic liquid piston, rotary screw, rotaryvane, scroll, diaphragm, air bubble compressors, etc. Further,compressors can be driven by a motor or the medium (e.g., bleed air,chamber discharge air, and/or recirculation air) via a turbine.

The heat exchanger 130 is a device built for efficient heat transferfrom one medium to another. Examples of heat exchangers include doublepipe, shell and tube, plate, plate and shell, adiabatic wheel, platefin, pillow plate, and fluid heat exchangers., air forced by a fan(e.g., via push or pull methods) can be blown across the heat exchangerat a variable cooling airflow to control a final air temperature of thebleed air.

The system 100 of FIG. 1A will now be described with reference to FIG.1B and FIG. 2, in view of the aircraft example. FIG. 1B is a diagram ofan schematic of a conventional bleed air driven environmental controlsystem 150 of an airplane utilizing a contemporary cabin three-wheel airconditioning system 151. FIG. 2 depicts a schematic of a system 200(e.g., an embodiment of system 100) as it could be installed on anaircraft.

The conventional bleed air driven environmental control system 150illustrates valves B1-V2, an inlet 152, a primary heat exchanger 154, acentrifugal compressor 156, a secondary heat exchanger 158, a condenser160, a water extractor 162, a reheater 164, a turbine 166, a cabin 168,a fan 172, a shaft 174, and a fan 176, each of which can be connectedvia tubes, pipes, and the like. Note that the contemporary cabinthree-wheel air conditioning system 151, also known as an airconditioning pack or a pack, includes components that are performingthermodynamic work, such as the centrifugal compressor 156, the heatexchangers 154, 158, the condenser 160, the water extractor 162, thereheater 164, and the turbine 166. The pack can also begin at a massflow control valve B1 and conclude as air exits the condenser 162.

The system 200 will now be describe with respect to a conventional bleedair driven environmental control system 150 of the airplane utilizing acontemporary cabin three-wheel air conditioning system 151. Theconventional bleed air driven air environmental control system 150receives bleed air at a pressure between 30 psia (e.g., during cruise)and 45 psia (e.g., on the ground) through the mass flow control valveB1. In the conventional bleed air driven air environmental controlsystem 150, during hot day ground operation, the centrifugal compressor156 of the contemporary cabin three-wheel air conditioning system 151receives nearly all of the flow of the bleed air at a pressure ofapproximately 45 psia. Further, during hot day cruise operation, thecentrifugal compressor 156 of the contemporary cabin three-wheel airconditioning system 151 receives only a portion of the flow of the bleedair at a pressure of 30 psia. The remainder of the bleed air bypassesthe centrifugal compressor 156 via a bypass valve B2 and is sent to thecabin 168. In addition, the conventional bleed air driven airenvironmental control system 150 can mix hot moist recirculation air E(represented by the dot-dashed line) with cold dry outside airdownstream of the conventional bleed air driven environmental controlsystem 150 in the cabin 168. This cool mixture is then used to conditionthe airplane's cabin and flight deck (i.e., the cabin 168 is supplied abulk average temperature of the mixed streams). Note that the outlettemperature of the contemporary cabin three-wheel air conditioningsystem 151 is driven well below the mix temperature because it needs tocool the recirculation air. In the conventional bleed air drivenenvironmental control system, driving the outlet temperature asdescribed is achieved by a combination of ram air cooling of the outsideair and pressure expansion across a turbine of the contemporary cabinthree-wheel air conditioning system 151. As a result, the conventionalbleed air driven environmental control system typically requires 30 psiaat its inlet. This requirement is in contrast to providing cabinpressurization and cooling at a high engine fuel burn efficiency, as theconventional bleed air driven environmental control system cannotutilize pressures near cabin pressure at the inlet of the contemporarycabin three-wheel air conditioning system 151.

In contrast to the conventional bleed air driven environmental controlsystem utilizing the contemporary cabin three-wheel air conditioningsystem 151, the system 200 is an example of an environmental controlsystem of an aircraft that provides air supply, thermal control, andcabin pressurization for the crew and passengers of the aircraft at ahigh engine fuel burn efficiency. The system 200 illustrates bleed airflowing in at inlet 201 (e.g., off an engine of an aircraft at aninitial flow rate, pressure, temperature, and humidity), which in turnis provided to a chamber 202 (e.g., cabin, flight deck, pressurizedvolume, etc.) at a final flow rate, pressure, temperature, and humidity.The bleed air can recirculate back through the system 200 from thechamber 202 (herein cabin discharge air and recirculated air arerepresented by the dot-dashed lines D1 and D2, respectively) to driveand/or assist the system 200.

The system in includes a shell 210 for receiving and directing ram airthrough the system 200. Note that based on the embodiment, an exhaustfrom the system 200 can be sent to an outlet (e.g., releases to ambientair through the shell 210). Note also that the system 200 can work withbleed pressures near a chamber pressure during cruise.

The system 200 further illustrates valves V1-V7, a heat exchanger 220,an air cycle machine 240 (that includes a turbine 243, a compressor 244,a turbine 245, a fan 248, and a shaft 249), a condenser 260, a waterextractor 270, and a recirculation fan 280, each of which is connectedvia tubes, pipes, and the like. Note that the heat exchanger 220 is anexample of the heat exchanger 130 as described above. Further, in anembodiment, the heat exchanger 220 is a secondary heat exchanger that isdownstream of a primary heat exchanger (not shown). Note also that theair cycle machine 240 is an example of the compressing device 120 asdescribed above.

The air cycle machine 240 extracts or works on the medium by raisingand/or lowering pressure and by raising and/or lowering temperature. Thecompressor 244 is a mechanical device that raises the pressure of thebleed-air received from the inlet 201. The turbines 243, 245 aremechanical devices that drive the compressor 244 and the fan 248 via theshaft 249. The fan 248 is a mechanical device that can force via push orpull methods air through the shell 210 across the secondary heatexchanger 220 at a variable cooling airflow. Thus, the turbines 243,245, the compressor 244, and the fan 248 together illustrate, forexample, that the air cycle machine 240 may operate as a four-wheel aircycle machine that utilizes air recirculated or discharged from thechamber 202 (e.g., in an embodiment, the air cycle machine 240 utilizeschamber discharge air to perform compressing operations, as indicated bythe dot-dashed line D1).

The condenser 260 is particular type of heat exchanger. The waterextractor 270 is a mechanical device that performs a process of takingwater from any source, such as bleed-air. The recirculation fan 280 is amechanical device that can force via a push method recirculation airinto the system 200, as indicated by dot-dashed arrow D2.

In a high pressure mode of operation of the system 200, high-pressurehigh-temperature air is received from the inlet 201 through the valve V1(mass flow control valve). The high-pressure high-temperature air entersthe compressor 244. The compressor 244 pressurizes the high-pressurehigh-temperature and in the process heats it. This air then enters theheat exchanger 220 and is cooled by ram air to produce cool highpressure air (e.g., at approximately ambient temperature). This coolhigh pressure air enters into the condenser 260 and the water extractor270, where the air is cooled and the moisture removed. The cool highpressure air enters the turbine 243, where it is expanded and workextracted. The work from the turbine 243 can drive both the compressor244 and the fan 248. The fan 248 is used to pull a ram air flow throughthe heat exchanger 220. Also, by expanding and extracting work on thecool high pressure air, the turbine 243 produces cold bleed air. Afterleaving the turbine 243, the cold bleed air is mixed at a mixing pointwith recirculation air D2 provided by the fan 280 through the valves V6and V7. The mixing point in this case can be referred to as downstreamof the compressing device 240, downstream of the compressor 244,downstream of the turbine 243, and/or upstream a low pressure side ofthe condenser 260. When applied to an air conditioning pack, the mixingpoint can be referred to as inside the pack. By mixing the cold bleedair with the recirculation air, the system 200 utilizes therecirculation air, which is warm and moist, to level out the cold bleedair (e.g., raise the temperature). This leveled out bleed air, in turn,enters a low pressure side of the condenser 260, cools the bleed air onthe high pressure side of the condenser 260, and is sent to conditionthe chamber 202.

Note that when operating in the high pressure mode, it is possible forthe air leaving the compressor 244 to exceed an auto-ignitiontemperature of fuel (e.g., 400 F for steady state and 450 F fortransient). In this situation, air from an outlet of the heat exchanger220 is ducted by the valve V2 to an inlet of the compressor 244. Thislowers an inlet temperature of the air entering the inlet of thecompressor 244 and, as a result, the air leaving the compressor 244 isbelow the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201bypasses the air cycle machine 240 via the valve V3 and mixes at amixing point with the recirculation air D2 provided by the fan 280through the valves V6 and V7 to produce mixed air. The mixing point inthis case can be referred to as downstream of the compressor 244 and/orupstream of the heat exchanger 220. When applied to an air conditioningpack, the mixing point can be referred to as inside the pack. The mixedair goes directly through the heat exchanger 220, where it is cooled byram air to the temperature required by the chamber 202, to produce coolair. The cool air then goes directly into the chamber 202 via the valveV5. Further, the chamber discharge air D1 is used to keep the air cyclemachine 240 turning at a minimum speed. That is, chamber discharge airD1 flowing from the chamber 202 through the valve V4 enters and expandsacross the turbine 245, so that work is extracted. This work is utilizedto turn the air cycle machine 240 at, for example, a minimum speed ofapproximately 6000 rpm. The air exiting the turbine 245 is then dumpedoverboard through the shell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is greaterthan approximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 mixes at a mixingpoint with the recirculation air D2 provided by the fan 280 through thevalves V6 and V7 to produce mixed air. The mixing point in this case canbe referred to as downstream of the compressor 244 and/or upstream ofthe heat exchanger 220. When applied to an air conditioning pack, themixing point can be referred to as inside the pack. The mixed air entersthe heat exchanger 220, where it is cooled by ram air to the temperaturerequired by the chamber 202 to produce cool air. The cool air then goesdirectly into the chamber 202 via the valve V5. Further, the cabindischarge air D1 is used to provide the energy to pressurize the bleedair entering the compressor 244. That is, the chamber discharge air D1flowing from the chamber 202 through valves the V4 enters and expandsacross the turbine 245, so that work is extracted. The amount of workextracted by the turbine 245 is enough to turn the air cycle machine 240at the speed required by the compressor 244 to raise a pressure of thebleed air to a value that can drive the bleed air through the heatexchanger 220 and into the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

The system 100 of FIG. 1A will now be described with reference to FIG.3, in view of the aircraft example. FIG. 3 depicts a schematic of asystem 300 (e.g., an embodiment of system 100) as it could be installedon an aircraft. Components of the system 300 that are similar to thesystem 200 have been reused for ease of explanation, by using the sameidentifiers, and are not re-introduced. Alternative components of thesystem 300 include a valve V8, a reheater 350, a condenser 360, and awater extractor 370, along with an alternative path for therecirculation air denoted by the dot-dashed line D3.

The reheater 350 and the condenser 360 are particular types of heatexchanger. The water extractor 370 is a mechanical device that performsa process of taking water from any source, such as bleed-air. Together,reheater 350, the condenser 360, and/or the water extractor 370 cancombine to be a high pressure water separator.

In a high pressure mode of operation, high-pressure high-temperature airis received from the inlet 201 through the valve V1. The high-pressurehigh-temperature air enters the compressor 244. The compressor 244pressurizes the high-pressure high-temperature and in the process heatsit. This air then enters the heat exchanger 220 and is cooled by ram airto produce cool high pressure air (e.g., at approximately ambienttemperature). This cool high pressure air enters into the reheater 350,where it is cooled; through the condenser 360, where it is cooled by airfrom the turbine 243; through the water extractor 370, where themoisture in the air is removed; and again into the reheater 350, wherethe air is heated to nearly an inlet temperature at the reheater 350.The warm high pressure and now dry air enters the turbine 243, where itis expanded and work extracted. The work from the turbine 243 can driveboth the compressor 244 and the fan 248. The fan 248 is used to pull ramair flow through the heat exchanger 220. After leaving the turbine 243,the cold air, typically below freezing, cools the warm moist air in thecondenser 360. Downstream of the condenser 360, the cold air leaving theair cycle machine 240 mixes at a mixing point with the recirculation airD3 provided by the fan 280 through the valve V8 to produce mixed air.The mixing point in this case can be referred to as downstream of thecompressing device 240, downstream of the compressor 244, and/ordownstream of the turbine 243. When applied to an air conditioning pack,the mixing point can be referred to as outside the pack. This mixed airthen sent to condition the chamber 202.

When operating in the high pressure mode, it is possible for the airleaving the compressor 244 to exceed an auto-ignition temperature offuel (e.g., 400 F for steady state and 450 F for transient). In thissituation, air from an outlet of the first pass of the heat exchanger220 is ducted by the valve V2 to an inlet of the compressor 244. Thislowers an inlet temperature of the air entering the inlet of thecompressor 244 and, as a result, the air leaving the compressor 244 isbelow the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201bypasses the air cycle machine 240 via the valve V3 and mixes at amixing point with the recirculation air D2 provided by the fan 280through the valve V6 to produce mixed air. The mixing point in this casecan be referred to as downstream of the compressor 244 and/or upstreamof the heat exchanger 220. When applied to an air conditioning pack, themixing point can be referred to as inside the pack. The mixed air goesdirectly through the heat exchanger 220, where it is cooled by ram airto the temperature required by the chamber 202 to produce cool air. Thecool air then goes directly into the chamber 202 via the valve V5.Further, the chamber discharge air D1 is used to keep the air cyclemachine 240 turning at a minimum speed. That is, chamber discharge airD1 flowing from the chamber 202 through the valve V4 enters and expandsacross the turbine 245, so that work is extracted. This work is utilizedto turn the air cycle machine 240 at, for example, a minimum speed ofapproximately 6000 rpm. The air exiting the turbine 245 is then dumpedoverboard through the shell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is greaterthan approximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 mixes at a mixingpoint with the recirculation air D2 provided by the fan 280 through thevalve V6 to produce mixed air. The mixing point in this case can bereferred to as downstream of the compressor 244 and/or upstream of theheat exchanger 220. When applied to an air conditioning pack, the mixingpoint can be referred to as inside the pack. The mixed air enters theheat exchanger 220, where it is cooled by ram air to the temperaturerequired by the chamber 202 to produce cool air. The cool air then goesdirectly into the chamber 202 via the valve V5. Further, the cabindischarge air D1 is used to provide the energy to pressurize the bleedair entering the compressor 244. That is, the chamber discharge air D1flowing from the chamber 202 through the valve V4 enters and expandsacross the turbine 245, so that work is extracted. The amount of workextracted by the turbine 245 is enough to turn the air cycle machine 240at the speed required by the compressor 244 to raise a pressure of thebleed air to a value that can drive the bleed air through the heatexchanger 220 and into the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

The system 100 of FIG. 1A will now be described with reference to FIG.4, in view of the aircraft example. FIG. 4 depicts a schematic of asystem 400 (e.g., an embodiment of system 100) as it could be installedon an aircraft. Components of the system 300 that are similar to thesystem 200 and system 300 have been reused for ease of explanation, byusing the same identifiers, and are not re-introduced. An alternativecomponent of the system 400 is a valve V9, along with the alternativepaths depicted.

In a high pressure mode of operation, high-pressure high-temperature airis received from the inlet 201 through the valve V1. The high-pressurehigh-temperature air enters the compressor 244. The compressor 244pressurizes the high-pressure high-temperature and in the process heatsit. This air then enters a first pass of the heat exchanger 220 and iscooled by ram air. The air exiting the first pass of the heat exchanger220 then enters the second pass of the heat exchanger 220 and is furthercooled to produce cool high pressure air. This cool high pressure airenters through the valve V9 the condenser 260 and the water extractor270, where the air is cooled and the moisture removed. The cool highpressure air enters the turbine 243, where it is expanded and workextracted. The work from the turbine 243 can drive both the compressor244 and the fan 248. The fan 248 is used to pull ram air flow throughthe heat exchanger 220. Also, by expanding and extracting work, theturbine 243 produces cold bleed air. After leaving the turbine 243, thecold bleed air is mixed at a mixing point with the recirculation air D2provided by the fan 280 through the valves V6 and V7. The mixing pointin this case can be referred to as downstream of the compressing device240, downstream of the compressor 244, downstream of the turbine 243,and/or upstream a low pressure side of the condenser 260. When appliedto an air conditioning pack, the mixing point can be referred to asinside the pack. By mixing the cold bleed air with the recirculationair, the system 200 utilizes the recirculation air, which is warm andmoist, to level out the cold bleed air (e.g., raise the temperature).This leveled out bleed air, in turn, enters the low pressure side of thecondenser 260, cools the bleed air on the high pressure side of thecondenser 260, and is sent to condition the chamber 202.

When operating in the high pressure mode, it is possible for the airleaving the compressor 244 to exceed an auto-ignition temperature offuel (e.g., 400 F for steady state and 450 F for transient). In thissituation, air from an outlet of the first pass of the heat exchanger220 is ducted by the valve V2 to an inlet of the compressor 244. Thislowers an inlet temperature of the air entering the inlet of thecompressor 244 and, as a result, the air leaving the compressor 244 isbelow the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201bypasses the air cycle machine 240 via the valve V3 and goes directlythrough the first pass of the heat exchanger 220. Upon exiting the firstpass, the bleed air then mixes at a mixing point with the recirculationair D2 provided by the fan 280 through the valves V6, V7 to producemixed air. The mixing point in this case can be referred to asdownstream of the compressor 244 and/or upstream of the second pass ofthe heat exchanger 220. When applied to an air conditioning pack, themixing point can be referred to as inside the pack. The mixed air entersthe second pass of the heat exchanger 220, where it is cooled by ram airto the temperature required by the chamber 202 to produce cool air. Thecool air then goes directly into the chamber 202 via the valve V9.Further, the chamber discharge air D1 is used to keep the air cyclemachine 240 turning at a minimum speed. That is, the chamber dischargeair D1 flowing from the chamber 202 through the valve V4 enters andexpands across the turbine 245, so that work is extracted. This work isutilized to turn the air cycle machine 240 at, for example, a minimumspeed of approximately 6000 rpm. The air exiting the turbine 245 is thendumped overboard through the shell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is greaterthan approximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 passes through thefirst pass of the heat exchanger 220 and then mixes at a mixing pointwith the recirculation air D2 provided by the fan 280 through the valvesV6, V7 to produce mixed air. The mixing point in this case can bereferred to as downstream of the compressor 244 and/or upstream of thesecond pass of the heat exchanger 220. When applied to an airconditioning pack, the mixing point can be referred to as inside thepack. The mixed air enters the second pass of the heat exchanger 220,where it is cooled by ram air to the temperature required by the chamber202 to produce cool air. The cool air then goes directly into thechamber 202 via the valve V9. Further, the cabin discharge air D1 isused to provide the energy to pressurize the bleed air entering thecompressor 244. That is, the chamber discharge air D1 flowing from thechamber 202 through the valves V4 enters and expands across the turbine245, so that work is extracted. The amount of work extracted by theturbine 245 is enough to turn the air cycle machine 240 at the speedrequired by the compressor 244 to raise a pressure of the bleed air tovalue that can drive the bleed air through the heat exchanger 220 andinto the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

The system 100 of FIG. 1A will now be described with reference to FIG.5, in view of the aircraft example. FIG. 5 depicts a schematic of asystem 500 (e.g., an embodiment of system 100) as it could be installedon an aircraft. Components of the system 500 that are similar to thesystems 200, 300, and 400 have been reused for ease of explanation, byusing the same identifiers, and are not re-introduced. An alternativecomponent of the system 500 is a valve V10, along with the alternativepaths depicted by the dot-dashed line D4.

In a high pressure mode of operation, high-pressure high-temperature airis received from the inlet 201 through the valve V1. The high-pressurehigh-temperature air enters the compressor 244. The compressor 244pressurizes the high-pressure high-temperature and in the process heatsit. This air then enters a first pass of the heat exchanger 220 and iscooled by ram air. The air exiting the first pass of the heat exchanger220 then enters the second pass of the heat exchanger 220 and is furthercooled to produce cool high pressure air. This cool high pressure airenters through the valve V9 into the reheater 350, where it is cooled;through the condenser 360, where it is cooled by air from the turbine243; through the water extractor 370, where the moisture in the air isremoved; and again into the reheater 350, where the air is heated tonearly an inlet temperature at the valve V9. The warm high pressure andnow dry air enters the turbine 243, where it is expanded and workextracted. The work from the turbine 243 can drive both the compressor244 and the fan 248. The fan 248 is used to pull ram air flow throughthe heat exchanger 220. After leaving the turbine 243, the cold air,typically below freezing, cools the warm moist air in the condenser 360.Downstream of the condenser 360, the cold air leaving the air cyclemachine 240 mixes at a mixing point with the recirculation air D4provided by the fan 280 through the valve V10 to produce mixed air. Themixing point in this case can be referred to as downstream of thecompressing device 240, downstream of the compressor 244, and/ordownstream of the turbine 243. When applied to an air conditioning pack,the mixing point can be referred to as outside the pack. This mixed airthen sent to condition the chamber 202.

When operating in the high pressure mode, it is possible for the airleaving the compressor 244 to exceed an auto-ignition temperature offuel (e.g., 400 F for steady state and 450 F for transient). In thissituation, air from an outlet of the first pass of the heat exchanger220 is ducted by the valve V2 to an inlet of the compressor 244. Thislowers an inlet temperature of the air entering the inlet of thecompressor 244 and, as a result, the air leaving the compressor 244 isbelow the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201bypasses the air cycle machine 240 via the valve V3 and goes directlythrough the first pass of the heat exchanger 220. Upon exiting the firstpass, the bleed air then mixes at a mixing point with the recirculationair D2 provided by the fan 280 through the valves V6, V10 to producemixed air. The mixing point in this case can be referred to asdownstream of the compressor 244 and/or upstream of the second pass ofthe heat exchanger 220. When applied to an air conditioning pack, themixing point can be referred to as inside the pack. The mixed air entersthe second pass of the heat exchanger 220, where it is cooled by ram airto the temperature required by the chamber 202 to produce cool air. Thecool air then goes directly into the chamber 202 via the valve V9.Further, the chamber discharge air D1 is used to keep the air cyclemachine 240 turning at a minimum speed. That is, the chamber dischargeair D1 flowing from the chamber 202 through the valve V4 enters andexpands across the turbine 245, so that work is extracted. This work isutilized to turn the air cycle machine 240 at, for example, a minimumspeed of approximately 6000 rpm. The air exiting the turbine 245 is thendumped overboard through the shell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is greaterthan approximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 passes through thefirst pass of the heat exchanger 220 and then mixes at a mixing pointwith the recirculation air D2 provided by the fan 280 through the valveV6 to produce mixed air. The mixing point in this case can be referredto as downstream of the compressor 244 and/or upstream of the secondpass of the heat exchanger 220. When applied to an air conditioningpack, the mixing point can be referred to as inside the pack. The mixedair enters the second pass of the heat exchanger 220, where it is cooledby ram air to the temperature required by the chamber 202 to producecool air. The cool air then goes directly into the chamber 202 via thevalve V9. Further, the cabin discharge air D1 is used to provide theenergy to pressurize the bleed air entering the compressor 244. That is,the chamber discharge air D1 flowing from the chamber 202 through thevalves V4 enters and expands across the turbine 245, so that work isextracted. The amount of work extracted by the turbine 245 is enough toturn the air cycle machine 240 at the speed required by the compressor244 to raise a pressure of the bleed air to value that can drive thebleed air through the heat exchanger 220 and into the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

In another embodiment, an environmental control system can operate in amultiple point mixing mode. The multiple point mixing mode, in general,mixes the first and second mediums (e.g., bleed air and recirculationair) at multiple points within the environmental control system. Thatis, during non-multiple point mixing mode operations, the amount ofrecirculation flow going to, e.g., the heat exchanger 220 can be 100%.Further, during the multiple point mixing mode operations, the amount ofrecirculation flow going to, e.g., the heat exchanger 220 can be lessthan 100% and the remaining amount of flow can proceed to another partof the environmental control system. In embodiments of the multiplepoint mixing mode, a first portion flowing to the heat exchange 220 canbe selected from a range of 50%-100% and a second portion flowing toanother part of the environmental control system can be a balance of thepercentage (e.g., 90/10 spilt; 80/20 spilt; 70/30 spilt; 60/40 spilt).The environmental control system can utilize the multiple point mixingmode, when at altitude while ram flow is not a desired temperature(e.g., too hot for proper cooling across the heat exchanger 220).

For example, when the environmental control system is operating in themultiple point mixing mode, the first and second mediums can be mixed attwo or more points. Note that the systems 200, 300, 400, 500 of FIGS.2-5 can operate in the multiple point mixing mode. For instance, whenany of the systems 200, 300, 400, 500 are operating in a low pressuremode or boost pressure mode, that system 200, 300, 400, 500 can alsooperate in the multiple point mixing mode.

For example, with respect to system 200 operating in the multiple pointmixing mode while in either the low pressure mode or the boost pressuremode, the recirculation air flowing from the fan 280 can be divided bythe valve V7, such that a first portion of the recirculation air flowproceeds to mix downstream of the compressor 244 (e.g., mix with bleedair to produce a combined air) and a second portion of the recirculationair flow proceeds to downstream of the turbine 243. The second portioncan then pass through the condenser 260 and mix with the combined airflowing through valve V5. Further, with respect to the system 400operating in the multiple point mixing mode while in either the lowpressure mode or the boost pressure mode, the recirculation air flowingfrom the valve V6 can be divided by the valve V7, such that a firstportion of the recirculation air flow proceeds to mix downstream of thecompressor 244 and before a second pass of the heat exchanger 220 (e.g.,mix with bleed air to produce a combined air) and a second portion ofthe recirculation air flow proceeds to downstream of the turbine 243.The second portion can then pass through the condenser 260 and mix withthe combined air flowing through valve V9.

For example, with respect to system 300 operating in the multiple pointmixing mode while in either the low pressure mode or the boost pressuremode, the recirculation air flowing from the fan 280 can be divided bythe valves V6 and V8, such that a first portion of the recirculation airflow proceeds through the valve V6 to mix downstream of the compressor244 (e.g., mix with bleed air to produce a combined air) and a secondportion of the recirculation air flow proceeds through the valve V8 todownstream of the turbine 243. The second portion can then mix with thecombined air flowing through valve V5. Note that the valves V6 and V8can be a plurality of valves working together as shown or as a singlevalve. Further, with respect to the system 500 operating in the multiplepoint mixing mode while in either the low pressure mode or the boostpressure mode, the recirculation air flowing from the fan 280 can bedivided by the valves V6 and V10, such that a first portion of therecirculation air flow proceeds through the valve V6 to mix downstreamof the compressor 244 and before a second pass of the heat exchanger 220(e.g., mix with bleed air to produce a combined air) and a secondportion of the recirculation air flow proceeds through the valve V10 todownstream of the turbine 243. The second portion can then mix with thecombined air flowing through valve V9. Note that the valves V6 and V10can be a plurality of valves working together as shown or as a singlevalve.

Aspects of the embodiments are described herein with reference toflowchart illustrations, schematics, and/or block diagrams of methods,apparatus, and/or systems according to embodiments of the invention.Further, the descriptions of the various embodiments have been presentedfor purposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments. The terminologyused herein was chosen to best explain the principles of theembodiments, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A system, comprising: an air conditioning pack; afirst medium; a second medium; a first mixing point located outside theair conditioning pack and configured to mix the first medium with thesecond medium; a second mixing point located inside the air conditioningpack and configured to mix the first medium with the second medium. 2.The system of claim 1, configured to operate in a first mode wherein thefirst and second medium are mixed at the first mixing point.
 3. Thesystem of claim 2, configured to operate in a second mode wherein thefirst and second medium are mixed at the second mixing point.
 4. Thesystem of claim 1, configured to operate in a first mode wherein thefirst and second medium are mixed at the second mixing point.
 5. Thesystem of claim 1, wherein the air conditioning pack comprises at leastone heat exchanger and at least one flow regulation device.
 6. Thesystem of claim 5, wherein the second mixing point is downstream of theat least one flow regulation device.
 7. The system of claim 6, whereinthe second mixing point is upstream of the at least one heat exchanger.8. The system of claim 7, wherein the at least one heat exchanger is aprimary heat exchanger.
 9. The system of claim 7, wherein the at leastone heat exchanger is a secondary heat exchanger.
 10. The system ofclaim 7, wherein the at least one heat exchanger comprises a pluralityof passes.
 11. The system of claim 10, wherein the second mixing pointis downstream of a first pass of the plurality of passes.
 12. The systemof claim 1, configured to operate in a first mode wherein the first andsecond medium are mixed at both the first mixing point and the secondmixing point.
 13. The system of claim 12, wherein a first portion of thesecond medium mixes with the first medium at the first mixing point toproduce a combined medium, and wherein a second portion of the secondmedium mixes with the combined medium at the second mixing point.
 14. Asystem, comprising: an air conditioning pack; a first medium; a secondmedium; a first mixing point located inside the air conditioning packand configured to mix the first medium with the second medium; a secondmixing point located inside the air conditioning pack and configured tomix the first medium with the second medium.
 15. The system of claim 14,wherein the air conditioning pack comprises at least one heat exchangerand at least one turbine.
 16. The system of claim 15, wherein the firstmixing point is downstream of the at least one turbine.
 17. The systemof claim 16, wherein the second mixing point is upstream of the at leastone heat exchanger.
 18. The system of claim 15, wherein the secondmixing point is upstream of the at least one heat exchanger.
 19. Thesystem of claim 15, wherein the at least one heat exchanger comprises aplurality of passes.
 20. The system of claim 19, wherein the secondmixing point is downstream of a first pass of the plurality of passes.21. The system of claim 16, configured to operate in a first modewherein the first and second medium are mixed at the first mixing point.22. The system of claims 21, configured to operate in a second modewherein the first and second medium are mixed at the second mixingpoint.
 23. The system of claims 16, configured to operate in a secondmode wherein the first and second medium are mixed at the second mixingpoint.
 24. The system of claim 14, configured to operate in a first modewherein the first and second medium are mixed at both the first mixingpoint and the second mixing point.
 25. The system of claim 24, wherein afirst portion of the second medium mixes with the first medium at thefirst mixing point to produce a combined medium, and wherein a secondportion of the second medium mixes with the combined medium at thesecond mixing point.